going2fast - 5/10/2010 3:17 PM
.......... again it only smokes a small amount every 5th or 6th shot id say and its driving pellets thru two sheets of 1/2"ply at 20 yards so it feels plenty powerful. i just cant figure out why the pattern moves around like it does. do you think this could be a bad seal? ive not had one of these apart before and it is still under warranty[ this is my second replacement as the first would not cock and i had to repair the second because the cocking arm bushing fell out. thanks for the help on that one] what would you do? send it back or buy a replacement seal and attempt to put it in? i do notice a fairly dramatic difference in where the pattern of the predators vs the crosmans at 20 yards. again they are decent patterns but several inches apart. is this normal? sorry for all the ?s. im new
Through two sheets of 1/2 inch ply at 20 yards ? Wow, not lacking for power ...or you've got some really poor quality plywood !!!
Mine smoked up until 300 pellets then I'd figured enough and opened it up. But, after the first 100 shots there was only smoke in the barrel, not coming out the muzzle, or the breach when opened. Still, the smoke wasn't lessening as fast as I would expect with a good seal, so I opened it up.
As Gene pointed out, the original harder nylon seals don't seal as well as the Maccari softer seals. Also, if there is an excessive amount of oil getting on the seal, chamber and piston, there is a slight negative pressure in the chamber when you cock the gun - (that "pressure drop" is how air gets pulled into the compression chamber). The faster you cock the gun the more negative pressure you make because of air resistance going in through the port in the compression chamber. Cock the gun quickly and you can still get some oil (and air) being sucked past a seal that isn't chewed up.
If you think about what's going on in there. The gun sits, and oil by it's nature likes to travel to areas of less oil. Shoot the gun, you use up some of the oil in the piston stroke (swept volume) area. Depending on seal damage or not, plus how fast you cock the gun, that can vary the amount of oil getting into the chamber. That's burnable "fuel" being introduced into the compression chamber in varying amounts, and as such, it can produce varying levels of pressure (power), thus not only varying speeds, but barrel vibration too, which can change POI. Let the gun sit again and the oil may not creep back in the same areas, or same amounts, each time because of changes in internal temperature affecting viscosity, and many other variable the gun is subjected to, etc. Sheesh !!! When you starting realy thinking about what can happen, when and how much, it's amazing we can get some of these piston guns to be anywhere near accurate at the best of times !!!

Good seal or bad, if it's still smoking after several hundered pellets, I'd say it's worth at least opening the gun to clean out all the excess oil, de-burr what you can, and then you can check the seal while your at it.
Just be VERY careful re-installing the seal past the threads in the rear end of the reciever. This has been well covered in some of the early threads about changing an XL's seal, and Super Streak seal too.
As far as differant pellets, through the same gun, having a differant POI (Point Of Impact), that's normal.
Paul.